Optically encoded information, such as bar codes, have become quite common. A bar code symbol consists of a series of light and dark regions, typically in the form of rectangles. The widths of the dark regions, the bars, and/or the widths of the light spaces between the bars indicates the encoded information. A specified number and arrangement of these elements represents a character. Standardized encoding schemes specify the arrangements for each character, the acceptable widths and spacings of the elements the number of characters a symbol may contain or whether symbol length is variable, etc.
To decode a bar code symbol and extract a legitimate message, a bar code reader scans the symbol to produce an analog electrical signal representative of the scanned symbol. A variety of scanning devices are known. The scanner could be a wand type reader including an emitter and a detector fixedly mounted in the wand, in which case the user manually moves the wand across the symbol. As the wand passes over the bar code, the emitter and associated optics produce a light spot which impacts on the code, and the detector senses the light reflected back from the light spot passing over each symbol of the code. Alternatively, an optical moving spot scanner scans a light beam, such as a laser beam, across the symbol; and a detector senses reflected light from the beam spot scanned across the symbol. In each case, the detector produces the analog scan signal representing the encoded information.
A digitizer processes the analog signal to produce a pulse signal where the widths and spacings between the pulses correspond to the widths of the bars and the spacings between the bars. The pulse signal from the digitizer is applied to a decoder which first determines the pulse widths and spacings of the signal from the digitizer. The decoder then analyzes the widths and spacings to find and decode a legitimate bar code message. This includes analysis to recognize legitimate characters and sequences, as defined by the appropriate code standard.
Different bar codes have different information densities and contain a different number of elements in a given area representing different amounts of encoded data. The denser the code, the smaller the elements and spacings. Printing of the small size denser symbols on an appropriate medium is exacting and thus is more expensive than printing large size low resolution symbols.
A bar code reader typically will have a specified resolution, often expressed by the size of its effective sensing spot. The resolution of the reader is established by parameters of the emitter or the detector, by lenses or apertures associated with either the emitter or the detector, by the threshold level of the digitizer, by programming in the decoder, or by a combination of two or more of these elements.
In a laser beam scanner, the effective sensing spot may correspond to the size of the beam at the point it impinges on the bar code. In a wand using an LED or the like, the spot size can be the illuminated area, or the spot size can be that portion of the illuminated area from which the detector effectively senses light reflections. By whatever means the spot size is set for a particular reader, the photodetector will effectively average the light detected over the area of the sensing spot. In one prior art example, U.S. Pat. No. 4,675,531 to Clark et al., an LED illuminates the bar code and images the code onto a photodetector. The aperture of the photodetector determines the resolution or "spot size." In the Clarke et al. system the photodetector effectively averages the light detected over the area of the aperture.
A high resolution reader has a small spot size and can decode high density symbols. The high resolution reader, however, may have trouble accurately reading low density symbols because of the lower quality printing used for such symbols. This is particularly true of symbols printed by a dot matrix type printer. The high resolution reader may actually sense dot widths within a bar as individual bar elements. In contrast, a low resolution reader detects an average intensity using a large spot size and can decode low density noisy symbols. However, a reader for relatively noisy symbols of low density, such as the dot matrix symbols, senses and averages such a wide spot that two or more fine bars of a high resolution symbol may be within the spot at the same time. Consequently, a reader having a low resolution, compatible with dot matrix symbols, can not accurately read high density symbols. Thus any reader having a fixed resolution will be capable of reading bar codes only within a limited range of corresponding symbol densities.
Commonly assigned U.S. patent application Ser. No. 07/735,573 filed Jul. 25, 1991, to Barkan et al., discloses a wand or scanner system for reading optically encoded information having a wide range of densities. The system includes either optical or electronic means to derive two or more channels of data from each scan pass of the wand or scanning beam over a bar code. Each channel of data has a different resolution, and the proposed system analyzes data from the two channels to obtain a valid result over a wide range of information densities. The optical and/or electronic solutions proposed in that application, however, are complex. The resulting system becomes costly, and the wand or scanner becomes larger and heavier due to the added components. A large, heavy handheld unit causes fatigue and discomfort when a user must hold and operate the unit for protracted periods.
Clearly a need exists in the art for a bar code reader which can be readily adapted to reading of bar codes over a wide range of symbol densities without adding undue complexity.
Another problem relates specifically to contact wand type bar code readers. Typically, such wands include an LED for emitting light to illuminate the bar code and a lens for focusing the widely divergent light from the LED onto the bar code. In many such wands, the lens is part of the actual tip of the wand, and consequently, the front surface of the lens contacts the surface on which the bar code is formed during scanning of the code symbols. Repeated use of the wand causes wear and scratching of the front surface of the lens. Such damage degrades the optical properties of the lens and reduces performance of the wand. As a result, the lens must be periodically replaced. Physical replacement of the lens, however, is time consuming and costly.
To alleviate these problems, a number of optical readers incorporate a keyboard and an alphanumeric display to form an integrated data entry terminal. These integrated terminals have included both contact wand type bar code readers and pistol grip type moving spot scanners. The data entry capabilities of such integrated terminals, however, have been limited by the nature of the keyboard and display.
A number of other types of data entry devices are known, and in many applications provide more convenient or "user friendly" data entry operation than do keyboards and alphanumeric displays. For example, a mouse allows a computer operator to move a cursor to point at an option illustrated on a display screen. The operator then "clicks" a button on the mouse to select the particular option. The mouse can also provide graphics data input. U.S. Pat. No. 4,906,843 to Jones et al. discloses a combination mouse and optical scanner, but the optical scanner scans characters or graphics data, not optically encoded information such as bar codes. The user manually scans characters by moving the mouse across the surface on which the characters appear.
A number of other keyboardless, data entry terminals have been proposed. U.S. Pat. No. 4,972,496 to Sklarew, for example, discloses a terminal device having a flat transparent input screen for generating input information when an operator contacts the screen with a stylus. A display screen mounted below the input screen displays symbols and graphic information drawn by the stylus. The operator inputs information into the associated computer through pen strokes essentially as if writing on a tablet with a pen. U.S. Pat. No. 4,916,441 to Gombrich discloses a handheld terminal including a non-contact point source type bar code reader and a touch sensitive display screen.
From the above discussion it should be clear that a need still exists to further develop various computer input devices integrated with means to scan optically encoded indicia which also provide convenient operation.